Stabilization of styrene



Dec. 3l, i940. s, Q FooRD STABILIZATION oF .sff'faaNE Filed Sept. ll, 1937 //V Vf /V 7 0R STNLE Y vGE ORGE FO0RD Patented Dec. 31, 1940 sTABlLlzAT'IoN 0F s'rYnENE Stanley George Foor. Londen, England,assignor to International Standard Electric vCorroration,

. New York, N. Y.

Application September 11, 1537 Serial No. 163,377

s claims. (ci. 26o- 91) This invention relates to stabilized styrene and to `a process for producing the same, wherein the formation of polymers thereof is retarded, more particularly during storage of the styrene. The

invention also relates to polymerized styrene produced from such stabilized styrene and to a process for producing such polymerized styrene.

A certain amountof knowledge exists as to substances which will stabilize monomeric styrenebut such knowledge is very incomplete. It has been stated that agents adapted substantially to prevent polymerization of styrene are substances which are mild oxidizing agents, and are identified as substances which do not give up their oxygen in gaseous form. This class Was stated to include quinone, mononitronaphthalene, trinitrotoluene,r nitrobenzene, dinitrobenzene, trinitrobenzene and derivatives of these compounds such as pikramid. An organic oxidizing agent containing a benzene nucleus in which oxygen replaces hydrogen atoms, and more particu- Iarly quinone has been suggested for the same purpose.- It was stated that each of these substances, including quinone, retards polymeriza- 254 tion up to a temperatureV of '170 C. but above this temperature'the action is reversed and the substances act as accelerators ofv polymerization. The proportion of quinone proposed to be used was from 0.25% `to 1% by weight of the styrene whether as such or in solution, and it was stated that distillation of 2 to 3 4hours at 140 C. inthe presence of 1% of quinone producesvnot more than 0.20.5%"po1ymer,whereas in the absence of quinone or similar material a similar distillation gives 20% polymer.

In the practice in accordancewith the above mentioned means for stabilizing styrene, it 4is necessary, before proceeding to carry out polymerizat-ion, to remove the stabilization agent, by some'such means as washing out with caustic soda solution or 'by distillation.

I have discovered, however, that the stabilization of styrene may be carried out by the addition of quinone in such manner that no distilla- 45 tion or washing is necessary when polymerization is desired, and that -the period of stabilization can be veryr closely controlled according to the amount of quinone added, the amounts necessary and desirable being very much smaller than pre-g. viously proposed.

I have discovered that the action of quinone upon styrene is not such as to prevent indenitely the polymerization of the styrene. vOn the contra'ry. when quinone is added' to -styrene a reaction takes place between quinone -and styrene resulting in the formation of a compound which h as no appreciable anti-catalytic eiect. Therefore, when all the quinone has been absorbed by this reaction, the polymerization of the styrene proceeds at approximately the same rate as in the absenceofany stabilizing agent. This reaction takes vplace very slowly at Aroom temperatures but much more rapidly at higher temperatures. The period during which nol poly-Y merization takes place may be termed the induction period. By the addition of quinone, therefore, the natural short time induction period of styrene at normal-temperatures may be prolonged, and/or an induction period caused to occur at temperatures at which itwould otherwise not occur. The percentages of rquinone needed for this Ipurpose are very small and the length of the induction period is dependent directly upon the amount of quinone yadded.` For the stabilization of styrene at room temperature, I

for example, from 0.005% to 0.05% of quinone may be added to the styrene, dependent upon the period of stabilization required. If it beethen desired to polymerizeth'e styrene before the conclusion of the period of stabilization, itisvonly necessary to heat the styrene for a comparatively brief Aperiod in order to destroy the stabilization Vaction of the`quinone.

For example, the induction period of' styrene containing 0.05% of quinone is minutes at 120 C.

Thus, if it be desired to polymerize the styrenev at a temperature of C.`or below, it is'only necessary to heat the styrene containing this percentage of quinone for one hour at*` 120 C. to destroy the stabilizing action of the quinone on the styrene almost completely. The ltime of heating required for a particular degree of polymeril zation is thus only a very short time longer than the normal period. Should it be desired'to polymerize the styrene at 120 C. it Will'be clear that the presence of 0.05% of quinone in the styrene prolongs the time of polmerization by the induc- Y tion period of '70 minutes only.

The luse of small amounts of quinone, from 0.005% to 0.05%, for stabilizing styrene, possesses considerable advantages over the use of the larger amounts hitherto thought necessary. The addition of appreciable quantities of 'quinone, to styrene raises-'the alternating current power factor 'of the material, both before polymerization and laf-ter. The rise in power factor caused by the addition of 0.25% to 1% of quinone is marked but with the small amounts'of quinone used in accordance withthe invention, this rise is inappreciable. Thus the power factor of monomeric styrene containing 0.05% of quinone is no higher than that of the styrene alone. The power factork the reaction product ofy styrenek with quinone, when 0.05% of quinone was added isno greater than in -the absence of the quinone. Furthermore, the product of the reaction between quinone and styrene when present in any but small quantity decreases the pliability of the polymerized product. This decrease is inappreof polymerized styrene containing ciable. when 0.05% of quinone hasbeenadded to the styrene but is appreciable with-0.25%

and over. This is a matter of importance. par- Y Product is to be end of the period when the time comes for poly-` merization. It will be readily understood that.

where it is desired to produce only that particular composition ofthe polymerized product that is produced by polymerization at a particular definite temperature corresponding precautionsy must be taken. .Thus if the temperature of polymerization required /is above room temperature,

an amount of quinone is added which is slightly v in excess of that required to stabilize for a given` period, in order to ensure that no polymerization occurs at room temperature prior to the brief heating period. yPure styrene Vremains stable at 25 C. (i. e. approximatelyroonr temperature) for about five weeks in the dark,` with 0.01% of quinone for not less than. 25 weeks, ywith 0.02% quinone for not less than 50 weeks, and with 0.05% quinone -for about 150 weellrs.'A If the temperature of ,polymerization required is above room temperature and below 120 C. it may be found advisable, in order to avoid too prolonged heating at the temperature, of polymerization, to heat at 120 C. for a period slightly below the induction period at that temperature-and then to reduce the temperature tothat of the desired l polymerization.

The curves in the accompanying'drawing show the elect of diii'erent quantities of quinone upon the course of polymerization of styrene at 120 C. Abscissae represent time in minutes and ordinates the logarithm of the relative viscosity, i. e'. of the ratio of the viscosity at the moment under oonsideration to the initial viscosity, which maybe taken as a measure of the degree of polymerization. Curve A shows the course of polymerization of styrene redistilled under reduced pressure. I

lhave found that if the styrene be saturated with hydroquinone at room temperature, the polymerization follows exactly the same curve. 'I'hus hydroquinone in such quantity has no effect in retarding the polymerization of pure styrene at 120 C. Curve B shows the course of polymerization of styrene to which 0.05% of quinone `has I been added. It will be observed that there is` an e induction period of less than minutes and that thereafter the polymerization proceeds at the same rate as for pure styrene. During the inducyellow colour of the quinonev tion period the deep gradually disappears as a slow reactionl with the styrene occurs forming a pale` yellowproduct. The end of the induction period coincides with the disappearance ofthe quinone colour. Curve C shows the course of polymerization oi' styreneto which 0.05% of quinone has been added, which has slight increase in the induction period than with quinone alone, butthe effect is of aminor order. Apparently hydroquinone was not taken up in any greater quantity than iscapable of solution in styrene itself since no green colour due to quinhydrone was apparent. Curve D shows the course of polymerization oi` styrene to which been shaken with hydroquinone. There is af 0.20%'of quinone has been added. It will be noted that there'is a considerable increase in the length ofthe induction period. so that the additional time of heating requiredbecomes uneconomic. It will be noted also that 'in curve D the rate of increase with time of the relative vis-.

cosity is less than with curves A, B and C. The rate` of increase'4 ofthe relative viscosity is only a true indication of the lrate of polymerization when the specific viscosity of the polymers formed is the same. In the case of curve D there is a slight fall in the speciilc viscosity ofthe polymer formed, and therefore the ,decrease in the slope of curve D is not entirely due to a decrease in the 'rate of` polymerization. Nevertheless, even 0.20%

of quinone has some effect in'slowing up the polymerimtion after theend of fthe induction period.

It. should Vbe noted `that if styrene hasr approached 'or even passed the end of its induction period during storage, the addition of amounts of monomeric styrene in the polymerized styrene formed fromthe monomeric styrene. Allv such plasticizing agents known to me are suchasdo not react with quinone and it is thereforeto be expected that the -20 quinoneaccordingto the invention prevents furpresence of a plasticizing agent does notinterw fere with the stabilizing action of quinone.v I have` verified the above inthe case of certain plasticizing agents. I have found, for example,

that the further addition of quinone to a mixture of by-volume of styrene and 10% of a chloriy nated diphenyl (which latter has been added to act as applasticizing agent)` produces an induction period of a magnitude which isr dependent only upon the amountjofquinone, and which is independent of' the presence ofV the chlorinated quinone has no appreciable diphenyl. Moreover, effect on the subsequent polymerization reaction, after the end of the induction period. It is to be understood that the vamount of quinone to be added for stabilizing such a mixture of styrene and plasticizing agent for a given period oi' time is based upon-the lweight of styrene present in the mixture. ,i j

What is claimed is: y y

1. Stabilized styrene containing .quinone but not more than 4about 0.05 stabilizing agent.l v I l 2. Polymerized styrene poiymerized from a stabilized 'styrene containing quinone but not more than about 0.05`precent of quinone.

3. 'Ihe process of stabilizing styrene to prevent substantial polymerization thereof during storage but without substantially decreasing the rate of polymerization thereof at v C. in comparison with the vrate of polymerization of unstabilized styrene at said temperature which comprises incorporating about 0.005 to 0.05 percent of quinone therein. l

STANLEY GEORGE FOORD.

percent of quinone as a.` 

